Oxygen wafted into Earth’s atmosphere earlier than thought

Date pushed back to 3 billion years ago

RUSTY BELT Red bands of oxidized iron run through ancient marine rocks in the Pongola river bed in South Africa. Scientists used these and other rocks to determine oxygen was present in Earth’s atmosphere nearly 3 billion years.

The date of Earth’s first whiff of oxygen may have occurred 300 million to 400 million years earlier than scientists thought. According to an analysis of ancient sediment, hints of oxygen graced the Earth’s atmosphere around 3 billion years ago.

The new date places oxygen on the Earth more than 600 million years before the Great Oxidation Event, when levels of atmospheric oxygen rose dramatically. In the last six years, a handful of geologic studies have dated transient wisps of oxygen to 2.6 billion to 2.7 billion years ago. Scientists think that photosynthetic microorganisms such as cyanobacteria produced the oxygen. So the timing of the first atmospheric oxygen has implications for how photosynthetic life evolved on the planet.

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